Abstract

Room temperature photoreflectance (PR) is shown to be influenced by optical interference between Si/SiGe/Si layers. The PR changes with wafer position due to a variation of Si cap thickness. By comparing the phase found from experiment with the theoretical phase calculated from the Seraphin coefficients, the thickness of the Si cap layer is determined across the wafer. Energies of the SiGe E1 and E1+ Delta1 critical point transitions found from room temperature PR measurements of thin strained SiGe layers are greater than expected. It is known that the SiGe interfaces are graded in composition, but this does not fully explain the energies found from the PR. Therefore, a simple square quantum well model is compared with experiment. It is likely that both composition grading and quantum confinement contribute to the energy shifts. Franz-Keldysh oscillations (FKO) are observed in room temperature PR spectra of InGaAsP and InP layers. Electro-modulation theory has been developed to fit the FKO. It is found that the InGaAsP spectra are best fitted when considering light and heavy holes. This is applied to the FKO from the InP layers, and a good match between experiment and theory is achieved. Energy transitions between electron and hole confined states in strained InGaAs quantum wells have been measured using room temperature PR and photoluminescence. The transition energies found from the PR have been compared with a theoretical quantum well model, and the band offsets found from the comparison. The agreement between experiment and theory is good for tensile strained InGaAs/InGaAsP quantum wells, and the band offset appeal's to vary little with tensile strain. A low energy feature in the PR spectra of InGaAs/InP quantum wells with compressive and tensile strain is attributed to a Zn impurity state. Despite difficulties in matching experiment with theory, the band offsets are also found for these structures.